Safety device for shutting down a turbine



P 1964 J. G. WILLIAMS 3,150,494

SAFETY DEVICE FOR SHUTTING DOWN A TURBINE JOHN CnWILLIAMS IN VEN TOR.

P 29, 1964 J. G. WILLIAMS 3,150,494

SAFETY DEVICE FOR SHUTTING DOWN A TURBINE Original Filed March 2. 1961 2 Sheets-Sheet 2 fi 74- E ii'll I 83 I 73 1 68 78 32 3 er 8g 3 4 24 +7 9| 69 x/ All/I I 1/ ll]? 63 6 FIG. 2

JOHN G-.WILL|AMS 8| INVENTOR.

FIG-3 Bygwpufiw United States Patent This invention relates to a safety device for a turbine. More particularly the invention relates to a safety device for shutting down a turbine of a feed water system.

This application is a continuation of my copending application Serial No. 92,893, filed March 2, 1961, now abandoned.

The typical feed water system used for example on a ship or in a power plant may include a condenser from which condensed steam is pumped to a deaerator. In the deaerator the water is heated from the exhaust steam of the turbine which also drives the feed pump which in turn introduces the water into the boiler. From the deaerator, heated water is caused to flow to the feed pump suction either by gravity head or by a separate pressure booster pump. The boiler turns the water back to steam, a part of which is delivered to the feed pump turbine from which exhaust steam passes to the deaerator to repeat the cycle.

Such systems are well known in the art and need not be explained further.

Heretofore these steam turbine driven feed water pump systems have used independent safety mechanisms associated with the suction side of the pump and the exhaust side of the turbine, which separate use has had inherent disadvantages, especially during rapid load transients.

The safety mechanism associated with the suction side of the pump is commonly a trip device which senses variations in the pump suction pressure and when this pressure drops below a predetermined minimum, the trip device causes shutoff of the steam supply to the feed pump turbine. This has happened even though the pump suction pressure was normally above the deaerator pressure by a constant and fixed amount and regardless of the fact that the variations in deaerator pressure caused corresponding changes in pump suction pressure.

This is very undesirable because there may be momentary sharp pressure drops in the deaerator caused by rapidly changing boiler loads, such as on a ship when during critical maneuvers the ship may go from full speed to crash stop and full reverse, which pressure drop would be sensed by the pump suction safety trip mechanism to thus cause a false shutoff. The false shutoff stops delivery of water to the boiler just at the time when the boiler is being fired to meet full load demand and consequently may cause the boiler to burn out. Furthermore the false shutoffs initiated by rapid pressure fluctuations in the deaerator occur even though there is an adequate supply of water available for the feed pump.

The usual safety mechanism associated with the turbine, a relief valve, might not operate for very long periods of time and therefore has a tendency to stick or malfunction when it finally is required to respond to excessive pressures in the turbine exhaust. If the exhaust pressure is high enough to cause rupture of the turbine casing operating personnel would be endangered by exposure to high temperature steam.

In order to understand the nature of the invention it is necessary to recognize that when the momentary sharp pressure drops occur in the deaerator due to changing boiler loads that there is a corresponding pressure drop in the turbine exhaust, this is so because the connecting line between the deaerator and the turbine exhaust is ice quite large and therefore exhaust steam velocities, which cause pressure loss, are very low. Furthermore, since turbine exhaust steam passes to the deaerator, as explained hereinbefore, it is also clear that a fixed diiference of pressure will normally exist between pump suction and turbine exhaust because the turbine exhaust pressure and the deaerator pressure are substantially the same. Thus, prior art safety devices caused shutoff of the turbine steam supply whenever the deaerator pressure dropped below the predetermined amount even though there be a simultaneous pressure drop in the pump suction pressure and the turbine exhaust pressure.

In View of the foregoing, it is evident that to avoid false shutdown by the low pump suction safety trip and to avoid a tendency toward sticking by the turbine exhaust pressure relief valve, the trip devices should:

(a) be sensitive to the difference of pressures between pump suction and turbine exhaust because this difference in pressure will remain constant even when the absolute deaerator pressure is changing rapidly.

(b) remain essentially at constant low temperature to avoid sticking caused by thermal distortion of moving parts, which is almost inevitable when such parts are exposed to varying high turbine exhaust steam temperatures (as the exhaust pressure relief valve is).

The improved safety device described and illustrated hereinafter accomplishes both of these objectives in a single mechanism.

An object of the invention is to provide an improved safety device which will overcome the prior art difficulties; which will prevent false shutoifs of the pump or turbine caused by momentary sharp pressure drops in the deaerator; which will be formed as a single safety device responsive to either excessive pressure of the turbine exhaust or low pump suction pressure caused by other than the momentary sharp pressure drops in the deaerator; which will operate satisfactorily regardless of a wide variation in deaerator static pressure; which being responsive to the differential pressure of the turbine exhaust and the pump suction is insensitive to rapid variations in deaerator pressure; which is trip-operated and must be manually reset.

Other objects and advantages will be apparent from the following description of one embodiment of the invention and the novel features will be particularly pointed out hereinafter in the claims.

In the drawings:

FIGURE 1 is a diagrammatic illustration of a feed water system in which the improved safety device is embodied.

FIGURE 2 is an enlarged sectional view of the improved safety device.

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 2.

In the embodiment of the invention illustrated in the drawings FIGURE 1 is a schematic showing a typical feed water system in which boiler 11 supplies steam through line 12 to turbine 14. Turbine 14 drives feed pump 16. Governor valve 13 regulates the admission of steam to turbine 14. The system here depicted is of the open type with deaerator feed tank 17 vented through orifices (not shown) to the atmosphere. Accordingly, exhaust steam from turbine 14 may be profitably employed in removing gases from water sprayed or otherwise disposed with a large surface in deaerator 17. Also this exhaust steam is used to heat the water in deaerator 17 to the temperature corresponding to the saturation pressure preset for deaerator 17. It will be clear to those skilled in the art and familiar with power plants that this safety device will be also applicable to closed feed water systems. Feed water generally comes from a condenser (not shown) to deaerator 17, the water is then delivered by booster pump 18 and feed pump 16 through feed line 19 to boiler 11. Of course, boiler 11 supplies steam via steam header 21 for conventional purposes additional to supplying the requirements of turbine 14. Turbine 14 only drives feed pump 16.

Position of governor valve 13 is regulated by a control means shown as fluid pressure operated mechanism 22. Oil or any other suitable working fiuid for mechanism 22 is energized by pump 23, passes through safety device 24 and is thence communicated to mechanism 22. Pump 23 usually delivers oil at pressures which vary inversely with changes in turbine speed as a conventional element in steam turbine control to maintain a predetermined speed.

Fluid operated mechanism 22 comprises casing 26 having diaphragm 27 operatively arranged therein and aligned to regulate governor valve 13 to an appropriate position corresponding to the balance reached between the pressure oil and spring 28. Diaphragm 27 is urged to open valve 13 by oil admitted under pressure through governor pipe 29 which oil is delivered through safety trip device 24.

The oil supplied to governor operating mechanism 22 is derived from pump 23 as stated hereinbefore. The oil is received by device 24 via inlet pipe 31 and is normally conducted therefrom to mechanism 22 via governor pipe 29. As described hereinafter, actuation of trip 24 will divert oil entering in line 31 to drain port 52 through which it will be returned to the oil reservoir, which is vented to the atmosphere.

Safety device 24 is illustrated more in detail in FIG- URE 2. The device comprises a housing 32 having a sleeve 33 in bore 34 thereof. Sleeve 33 has bore 36 in which valve plug 37 is disposed. Valve plug 37 is provided with lands 38 and 39 separated by connecting spindle 41. Sleeve 33 is provided with passage 42 that communicates with inlet port 43 in the housing to which inlet pipe 31 is connected. Sleeve 33 is also provided with passage 44 which communicates with governor port 46 in the housing to which governor pipe 29 is connected. Sleeve 33 has annular grooves 47 and 48 that communicate with inlet 43 and governor 46 ports, respectively. Annular grooves 49 in the region of land 39 are also provided in sleeve 33. The sleeve is ported at annular groove 49 and is connected to drain port 52 which leads back to the reservoir of oil to which the intake of pump 23 is connected.

Sleeve 33 is further provided with annular groove 53 located to the right of inlet port 43 and that groove connects to sleeve bore 36 with passage 54 leading to drain port 52 by means of holes (not shown). Thus any oil which leaks toward the right end of valve plug 37 is conducted to drain port 52.

The right hand end of valve plug 37 is connected by pin 56 to slide 57 disposed in bore 34. The end of slide 57 to which valve plug 37 is connected is adapted to accommodate trigger 58 that is pivotally supported by pin 59. Trigger 58 is urged clockwise against stop pin 61 by slide button 62 and spring 63 housed in bore 64. Spring 63 is held in compression against slide button 62 by means of a screw plug which is secured in position by a pm.

Slide 57 is urged to the left by thrust means shown as compression spring 66 disposed about slide 57 and within housing bore 34. Spring 66 is held in compression by a cap secured to the right end of housing 32.

When valve plug 37 is in the off position shown in FIGURE 2 inlet port 43 is closed and the fluid operated mechanism 22 is connected through governor port 46 to drain port 52. When valve plug 37 is pulled to the right by means of a hand wheel or knob to the on position wherein land 38 is to the right of inlet port 43, inlet port 43 is communicated with governor port 46 and consequently to pressure fluid operated mechanism 22.

In order to hold valve plug 37 in its on position a retaining means shown as trigger keeper 67 is provided. Keeper 67 is slidably disposed in sleeve 68, the lower end of which is secured to base plate 69 and the upper end of which is housed within accordion bellows 71 which serves as a pressure movable member and divides housing element 74 into water chamber 72 and balancing chamber 73. Bellows 71 is embraced by housing element 74 the upper end of which is closed as shown and the lower open end of which is mounted in pressure-tight relationship with a flange 76 secured to mounting plate 77. Mounting plate 77 is carried by spacer 87 through which bolts 81 extend and are threaded into base plate 69 and housing element 32.

The upper end of bellows 71 is secured by welding or otherwise to a bearing member 79 into which trigger keeper 67 extends. Trigger keeper 67, which in combination with other members serves as a means to actuate the closing of governor valve 13, is urged upwardly by compression spring 83 disposed about sleeve 68. The upper end of spring 83 bears against bearing member 79 and the lower end is supported on an adjustable sleeve 84 by means of which the initial compressor strain is imparted to spring 83 and the pressure at which trigger 58 is released may be thus adjusted. For the purpose of adjustment the lower end of sleeve 68 is provided with wrench sockets 86.

As seen in FIGURE 3 removal of cover 87 permits access to wrench socket 86.

The pressure in exhaust line 88 of turbine 14 is communicated to balancing chamber 73 via steam pressure registering means shown as conduit 89 and passage 91. Exhaust line 88 as stated hereinbefore is of sufiicient size, usually 6" or larger, so that the deaerator and turbine exhaust pressures correspond to one another at all times during operation of the feed water system.

In operation, one way of activating safety device 24 is by an excess of pressure in balancing chamber 73 inside bellows 71. This will cause bellows 71 to elongate thereby moving trigger keeper 67 upward to release trigger 58. Upon release of trigger 58 compression spring 66 displaces valve plug 37 leftward to its off position shutting inlet port 43 as shown in FIGURE 2. Port 46 which connects with diaphragm casing 26 of mechanism 22 is communicated with oil drain port 52 via governor pipe 29 to reduce the oil pressure on diaphragm 27 to atmosphere thereby permitting spring 28 to shut turbine governor valve 13.

The pressure at inlet or suction side 92 of feed pump 16 is communicated to water chamber 72 via water pressure registering means shown as conduit 93. Housing element 74 is provided with inlet fitting 94; water pressure at inlet or suction side 92 of feed pump 16 is communicated to water chamber 72 causing bellows 71 to be compressed and trigger keeper 67 to be maintained in engagement with trigger 58.

Consequently when the pressure at inlet 92 of feed pump 16 is at or beyond a safe level and slide 57 is pulled to the right, the pressure differential acting across bellows 71 will move keeper 67 downwardly until its notched end engages the end of trigger 58. When the trigger is so engaged, valve plug 37 is held in an on or open position. So long as valve plug 37 is in an on or open position, pressure oil is communicated from port 43 to port 46 to permit pressure fluid operated mechanism 22 to regulate governor valve 13, which valve is always open at normal speeds. However, another way of activating safety device 24 is when the pressure at inlet 92 of feed pump 16 drops below the preset level it will cause bellows 71 to elongate and approach the position shown in FIGURE 2. Thus notched end of trigger keeper 67 will disengage from the end of trigger 58 and valve plug 37 will be moved to the right to its off position as shown in FIGURE 2. Then the pressure oil to diaphragm 27 is shut ofl? and governor valve 13 is closed by the action of spring 28.

At this point it is important to note that actuation of the improved safety device 24 is effected by a reduction of a pressure difference between chambers 72 and 73 to a point where keeper 67 is caused to move upward and thus effect closure of governor valve 13 as described hereinbefore. Reduction of pressure in chamber 72 while pressure in chamber 73 is constant; or increase of pressure in chamber 73 while pressure in chamber 72 is constant can in either case effect closure of governor valve 13. If the pressures in both chambers 72 and 73 rise or fall simultaneously in almost equal amounts actuation of safety device 24 does not occur. During rapid load transients the pressures in deaerator 17 (same as turbine exhaust pressure) and the pressure in pump suction 92 will rise or fall in equal amounts because the pressure generated by pump 18 is normally constant. Consequently, this safety device is insensitive to the effect of rapid load changes which causes fluctuation of pressure in deaerator 17 i Safety device 24 will respond only to failure of pump 18 to produce adequate pressure to pump 16 while turbine exhaust pressure is constant and only to a rise in turbine casing exhaust pressure while pressure to pump 16 is constant. A rise in turbine exhaust pressure is usually caused by maloperation of the turbine at star-ting. This situation could occur if governor valve 13 is opened by manual operation of pump 23 while the valve (not shown) in turbine exhust line 88 remains closed. The correct procedure is to open the exhaust valve first at startup before causing governor valve 13 to open. In sub-stance, safety device 24 is sensitive only to deviation from the norm of the pressure difference between pressure to pump 16 and exhaust from turbine 14 and is insensitive to extraneous pressure surges in the parts of the steam cycle.

As stated hereinbefore, existing devices which respond to a drop in pump suction pressure will cause closure of valve 13 when the pressure in deaerator 17 falls because at this time the pressure to pump 16 will drop also and this situation will endanger boiler 11. Actually, closure of valve 13 and consequent shutdown of pump 16 is not Wanted when and only when the pressures to pump 16 and in deaerator 17 (turbine exhaust) drop simultaneously.

It will also be noted that this safety device is located remotely fiom turbine 14 and therefore is not subject to the high temperatures associated with such turbines. By condensation, line 89 is filled with water in the vicinity of safety device 24. For this reason safety device 24 operates at almost constant low temperature which avoids malfunctioning due to thermal distortion of close fitting parts. This situation is quite different from current turbine exhaust pressure relief valves which are always exposed to high fluctuating turbine exhaust temperatures and are therefore subject to malfunctioning due to thermal distortion of close fitting parts.

Since safety device 24 will protect turbine 14 from high excessive exhaust pressure, present usage of expensive excess pressure relief valves in the turbine exhaust line can be eliminated to effect both cost reduction and reliability improvements.

Valve plug 37 cannot be reset in an on or open position until the condition which caused the high exhaust pressure or low feed pump inlet pressure has been corrected. It is highly significant that the present device must be reset every time the feed pump is started. Resetting gives an assurance that the device is in working order.

It will be understood that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the claims.

What is claimed is:

1. A safety device for shutting down a turbine of the water feed system, the turbine receives operative steam through a line from a boiler and exhausts steam through a line to a deaerator, the deaerator is connected by a line to the inlet of a feed pump which discharges the water through a line into the boiler, the line between the boiler and the turbine has a normally open oil-operated control valve therein, the safety device is disposed in the line delivering oil to the control valve and comprising:

(a) a housing having a pressure difference force balancing chamber formed therein,

(b) a trigger-operated valve operatively associated with said safety device and in a normally open position,

(0) a trigger keeper normally in engagement with said trigger-operated valve to prevent closing thereof,

(d) said pressure difference force balancing chamber in communication with the pres-sure from the turbine exhaust steam and from the pump suction,

(e) a spring means in said pressure difference force balancing chamber to balance the pressure difference force therein,

(1) said trigger keeper operatively disposed in said pressure difference force balancing chamber and on a rise in turbine exhaust steam pressure or a fall in pump suction pressure the force balance will be upset and the trigger keeper will be displaced out of operative engagement with said trigger-operated valve.

2. The combination claimed in claim 1 wherein (a) a trigger in said trigger-operated valve normally engaged by said trigger keeper to prevent closing of said trigger-operated valve,

(b) the pressure difference force balancing chamber including a bellows forming a chamber on each side thereof with one chamber having turbine exhaust steam pressure therein from the turbine and the other chamber having the suction pressure therein from the pump, the pressure difference being established by a presetting of the manually adjustable spring force,

(c) a member in the pressure difference force balancing chamber engaging the trigger keeper to normally urge it to engage the trigger and adapted to urge the trigger keeper to disengage from the trigger on the force balance being upset by a rise in turbine exhaust steam pressure or a fall in pump suction pressure.

3. A safety device for a boiler feed system operatively associated with a turbine and feed pump, the turbine delivers exhaust steam to a deaeraor to heat Water therein before it is introduced into the pump, the safety device is disposed in the oil line of the steam governor valve of said turbine and comprising:

(a) a housing having a chamber formed therein,

(b) a bellows disposed in said chamber having one end thereof connected to said housing forming chamber means on each side of said bellows,

(0) one of said chamber means communicating with the pressure from the steam exhaust of said turbine and the other of said chamber means communicating with the pressure from the suction side of said feed pump,

(d) a trigger-operated valve having a trigger and disposed in said housing in said chamber,

(e) a trigger keeper connected to and movable with said bellows at the end thereof remote from the bellows connection to said housing,

(f) said trigger keeper to normally engage said trigger and adapted to disengage said trigger to close said governor valve when said trigger keeper and the end of the bellows moves in a direction away from said trigger responsive to a change in the pressure force balance in said balancing chamber.

4. The combination claimed in claim 3 wherein the line connecting the turbine and the deaerator is sufficiently large so that the pressure at the turbine exhaust is substantially equal to the pressure in the deaerator adjacent the line connection so that a sudden sharp drop in absolute pressure in the deaerator will result in a corresponding pressure drop at the turbine exhaust.

5. The combination claimed in claim 4 wherein said safety device is located remote from said turbine whereby thermal distortion of said safety device caused by heat from said turbine is avoided.

6. In combination, a boiler, a feed Water system having a feed pump including a suction inlet communicating with a source of water and an outlet communicating with said boiler, a steam turbine including a steam inlet and a steam exhaust which exhaust is delivered to a deaerator, said steam turbine connected to drive said boiler feed pump, a governor valve operatively disposed relative to said steam inlet to control the supply of steam to said turbine, control media for regulating said governor valve, a safety device comprising a housing, a bellows member connected in said housing to form a Water chamber and a pressure difference force balancing chamber therein, a spring means operatively associated in said balancing chamber, actuating means connected to said bellows member and movable therewith, said actuating means operatively associated with said control media to stop the steam flow therethrough on elongation of said bellows member beyond a predetermined distance to reestablish a force balance by means of the opposing spring in said balancing chamber whereby said governor valve will be caused to close, a first conduit means for communicating the pressure water at said suction inlet of the feed pump with said water chamber whereby on fallolf of said water pressure said bellows member will elongate to actuate said activating means to stop the flow of said control media, a second conduit means for communicating the pressure steam at said steam exhaust of the turbine with said balancing chamber whereby on increase of said steam pressure said bellows member will be elongated to actuate said activating means to stop the flow of said control media.

References Cited in the file of this patent UNITED STATES PATENTS 2,425,958 Schellens et al. Aug. 19, 1947 2,842,151 Cunningham et al. July 8, 1958 

6. IN COMBINATION, A BOILER, A FEED WATER SYSTEM HAVING A FEED PUMP INCLUDING A SUCTION INLET COMMUNICATING WITH A SOURCE OF WATER AND AN OUTLET COMMUNICATING WITH SAID BOILER, A STEAM TURBINE INCLUDING A STEAM INLET AND A STEAM EXHAUST WHICH EXHAUST IS DELIVERED TO A DEAERATOR, SAID STEAM TURBINE CONNECTED TO DRIVE SAID BOILER FEED PUMP, A GOVERNOR VALVE OPERATIVELY DISPOSED RELATIVE TO SAID STEAM INLET TO CONTROL THE SUPPLY OF STEAM TO SAID TURBINE, CONTROL MEDIA FOR REGULATING SAID GOVERNOR VALVE, A SAFETY DEVICE COMPRISING A HOUSING, A BELLOWS MEMBER CONNECTED IN SAID HOUSING TO FORM A WATER CHAMBER AND A PRESSURE DIFFERENCE FORCE BALANCING CHAMBER THEREIN, A SPRING MEANS OPERATIVELY ASSOCIATED IN SAID BALANCING CHAMBER, ACTUATING MEANS CONNECTED TO SAID BELLOWS MEMBER AND MOVABLE THEREWITH, SAID ACTUATING MEANS OPERATIVELY ASSOCIATED WITH SAID CONTROL MEDIA TO 